I was excited to see squirrels, lightning bugs and a racoon in the US.
When people come to Australia they obviously want to see kangaroos, koalas and platypus and quokka. Koalas are very rare to see in the wild, and a visit to a zoo will score you a sleeping ball on a branch. Kangaroos are frequently roadkill if you go outside the city. Quokka require a long trip to a really remote location. You'll also almost never see a platypus, even the ones at the zoo you might catch a water ripple at best.
But if you're headed to Sydney city, guaranteed you'll spot the almighty and much maligned "bin chicken", our Australian white ibis. Often not quite white from the bins. At night they serenade you with their collective honking from their tree, which can be easily spotted by the masses of white poop underneath. And you'll see fruit bats in the evening. Hopefully not the daytime corpses hanging from electrical cables while they slowly rot, but that's not altogether unlikely either, unfortunately.